This invention generally relates to an electrophotographic printing machine, and more particularly concerns a printing machine arranged to reproduce transparencies or opaque original documents.
The process of electrophotographic printing comprises exposing a charged photoconductive member to a light image of an original document being reproduced. The irradiated areas of the photoconductive surface are discharged to record thereon an electrostatic latent image corresponding to the original document. A development system moves a developer mix of carrier granules and toner particles into contact with the photoconductive surface. The toner particles are attracted electrostatically from the carrier granules to the latent image forming a toner powder image thereon. Thereafter, the toner powder image is transferred to a sheet of support material. After transferring the toner powder image to the sheet of support material, a fusing device permanently affixes the toner powder image thereto. The foregoing briefly describes the basic operation of an electrophotographic printing machine. This concept has mechanized by a wide variety of machines. However, in most instances, the prior art machines have various types of improvements which provide greater copy clarity. These improvements are all of a nature such that specific problems have been resolved. In addition, special purpose electrophotographic printing machines have been developed and are in wide commercial use. For example, electrophotographic printing machines are presently commercially available for reproducing microfilm. Machines of this type are described in U.S. Pat. No. 3,424,525 issued to Towers et al., in 1969; U.S. Pat. No. 3,542,468 issued to Blow, Jr., in 1970; and U.S. Pat. No. 3,547,533 issued to Stokes et al., in 1970. In general, a microfilm reproducing machine produces an enlarged copy of a microfilm original. However, it has been found to be difficult to produce copies having pictorial quality. Moreover, high quality reproduction of color slides has only been recently achieved. This is described in co-pending application Ser. No. 540,617 filed in 1975. As described therein, a light image of a color transparency is projected onto a mirror. The mirror reflects the light image in a downwardly direction through a screen and field lens onto the charged portion of the photoconductive surface. This light image is filtered to produce a single color electrostatic latent image on the photoconductive surface. Successive single color electrostatic latent images are recorded on the photoconductive surface and developed with the appropriately colored toner particles. These toner powder images are transferred to a sheet of support material in superimposed registration with one another. This multi-layered toner powder image is then permanently affixed to the sheet of support material forming a copy of the color slide being reproduced. However, a machine of this type requires numerous manual manipulations in order to convert it from reproducing opaque copies to one which reproduces slides. For example, the platen cover must be moved away and a mirror positioned in the path of the transparency light image to direct the light image onto the charged portions of the photoconductor member. No simple structure has been developed for readily achieving the foregoing. This increases the complexity of using a printing machine employed to reproduce color slides.
Accordingly, it is a primary object of the present invention to improve an electrophotographic printing machine arranged to reproduce color transparencies by simplifying the conversion thereof from the opaque copying mode to the transparency copying mode.